Automatic controls for ventilation equipment are customarily designed to operate the ventilation equipment when the temperature inside of a building exceeds a certain predetermined temperature. When the temperature is below the predetermined level, the ventilation equipment does not operate. When the temperature exceeds the predetermined level, the ventilation equipment is started in operation and its operation continues until the temperature drops to either the predetermined level or to some other control level. Since ventilation can help in cooling a home, building, or other structure whenever the interior temperature exceeds the exterior temperature, it is desirable to have apparatus and methods for automatically causing fan operation whenever the interior temperature exceeds the exterior temperature by just a few degrees. It is also desirable, especially during winter, to control humidity within a home, building, or other structure by ventilation. This invention seeks to solve both the temperature and humidity problems by providing ventilation whenever it is needed in response to relatively elevated inside temperature and in response to excessive interior humidity.